The present invention relates to a method for forming a gel in an underground formation surrounding a wellbore for the purpose of decreasing permeability in the formation. More particularly, the invention concerns an in situ formed gel of hydroxy propyl cellulose, an alkali metal dodecyl sulfate and brine.
Poor vertical conformance and excessive water production are two problems which afflict most hydrocarbon producing formations. Because of different geological strata having varying permeabilities, fluids injected into and produced from hydrocarbon formations tend to preferentially channel into strata of relatively high permeability. Thus, enhanced oil recovery fluids bypass large concentrations of hydrocarbons and flow through strata that have already been swept of hydrocarbons. This also results in uneconomically high water to oil ratios from producing wells.
Numerous processes have been proposed to alleviate preferential channeling through formation strata of relatively high permeabilities. Most methods involve the injection of an externally formed or in situ formed gel to lower permeability. U.S. Pat. Nos. 4,412,028; 4,494,606; 4,498,539; 4,503,912; 4,561,502 and 4,579,667 all describe the injection of polyacrylamide gels into a formation for profile control. Some polyacrylamide gels suffer from a lack of stiffness. They soften and do not always stay where placed. Polyacrylamides also have limited stability under acidic conditions.
Because of their structure and inexpensive cost, lignins and lignosulfonates have been frequently used to form permeability reducing gels. Reissue Pat. No. 30,767 and U.S. Pat. No. 4,074,757 set lignosulfonate and water gels by high formation temperatures. Other lignin or lignosulfonate gel patents include U.S. Pat. Nos. 3,896,827; 4,257,813; 4,275,789; 4,296,814; 4,428,429; 4,110,231; 3,985,659 and 4,322,301.
Hydroxy propyl cellulose has been evaluated for different uses in the oil field. It has been screened for polymer flooding applications, but has not been used extensively because of its generally higher cost. See Szabo, M. T., "An Evaluation of Water-Soluble Polymers for Secondary Oil Recovery-Part 1," Journal of Petroleum Technology, 1979, p. 553-560.
Gel systems have been formulated using hydroxy propyl cellulose and a suitable cross-linking agent such as titanium, zirconium or antimony. U.S. Pat. Nos. 4,378,049; 4,553,601 all disclose such gel systems with cross-linking agents.
U.S. Pat. No. 4,627,494 describes a method of using hydroxy propyl cellulose as a sacrificial agent for surfactant floods. Water-soluble suspensions of hydroxy propyl cellulose and other polymers are disclosed in European Patent Application No. 81301140.0.
British Petroleum has published a report that describes their efforts to develop a "sea water soluble precipitable polymer" for use in the North Sea. A large slug of hydroxy propyl cellulose was required to achieve a small permeability reduction. See Graham, D. E. et al., "Treatment Fluids to Improve Sea Water Injection," New Technologies for the Exploration and Exploitation of Oil and Gas Resources, Graham and Trotman, Vol. 2, 1984, p. 860-872.
U.S. Pat. No. 4,169,818 and 4,172,055 disclose the use of hydroxy propyl cellulose with polymaleic anhydride derivatives to form a fluid with increased viscosity. The references disclose use as a hydraulic fluid in well drilling operations.